Date of Award

2007

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Forest Resources

Advisor

William H. Livingston

Second Committee Member

Seanna L. Annis

Third Committee Member

David R. Houston

Abstract

In 2003, Forest Inventory and Analysis (FIA) data showed a 30% increase in beech mortality since 2002 in northern Maine. By 2006, most affected plots sampled were averaging 47% mortality across the northern region. This mortality followed one of the most severe drought periods in northern Maine in over a century. In addition, beech bark disease (BBD) has been present in Maine since 1931. The disease requires prior infestation of an exotic scale insect, Cryptococcus fagisuga (Lind.), to permit infection by one or more fungi, primarily Neonectria ditissima (Tul. & C.Tul.) Samuels & Rossman and Neonectha faginata Castlebury et al.. The primary hypotheses of this thesis were (i) scale populations increased such that reductions in radial growth of beech could be measured prior to 2003 when a sharp increase in beech mortality occurred across northern Maine; (ii) onset of growth reductions and/or mortality in beechcoincide with drought based on examining temporal and spatial relationships of hydrological data (precipitation, streamflow records) and tree ring patterns across the region; (iii) mortality is influenced by a combination of specific plot and tree-level factors. To evaluate these hypotheses, 46 fixed radius plots were randomly located across four delineated bioregions in northern Maine. Tree cores from both beech and an associated species were collected from both high and low mortality sites to evaluate the radial growth response following drought and the onset of disease in beech. Additionally, fungal samples were taken from dead and dying trees to evaluate the spatial distribution of fungi throughout this region. The drought period from 1999-2002 coincided with the onset of growth decline in all species, accelerated growth decline in beech, and a significant increase in beech mortality across all regions. Two simultaneous killing phases occurred across northern Maine from 1999-2004. The first killing phase was a front along the Maine-Quebec border (bioregion 1) in stands never before affected by BBD. Mild winter temperatures after 2000 coincide presumably with scale establishment and buildup in this region. However, high autumn rainfall between 2003-2005 would have drastically reduced scale populations by the time mortality became apparent. A second killing phase occurred further east and south where scale and Neonectria were already present on diseased trees having limited cankers. This is the first report of a second killing phase of beech within the "aftermath" forests of Maine. Ascospore measurements from 201 bark disks containing perithecia as well as isolates across all regions generally support the hypothesis that, once established, Neonectria faginata dominates the BBD complex. However, stands did contain high levels (>30%) of Neonectria ditissima if other highly susceptible tree species were present (R2=0.717). Severe drought can help incite widespread mortality when BBD is present. The fate of these northern forests depends on whether a new cohort of equally susceptible beech sprouts develops. If drought was successful in killing root systems, then beech will be gradually displaced by other species. If not, beech will continue to persist until enough coincidental factors overlap once again to permit new infections and mortality.

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